Most thermostatic controllers in a building simply establish a single temperature level for either the heating or air-conditioning unit then in operation. In a heating system, the thermostat turns-on the furnace when the temperature falls below the set level and turns it off when the temperature exceeds it. In a cooling system, the thermostat turns-off the cooling unit when the temperature falls below the set level and turns it on when the temperature exceeds it.
For ideal comfort or for energy conservation reasons, it is common to reduce the degree of cooling or heating desired during sleeping hours. This has generally required a manual change in the thermostat setting.
A recent commercial thermostat has attempted to automatically effectuate a reduction in the operation of these units at night. However, adjusting the times at which the temperature levels change requires a complicated series of manipulations of delicate parts. The first step involves accurately setting a special clock to the correct time of the day. Next, a first timer pointer is adjusted to the exact time on a dial at which the thermostat should switch to the higher temperature level. Then, a second timer pointer is adjusted to the exact time on the same dial at which the thermostat should switch to the lower temperature level. Instructions specifically point out the need for setting the pointers to the correct half of the day; this follows since "10:00" appears in both the morning and the evening. Changing the time for either occurrence, of course, involves resetting the pointer to, hopefully, the correct position on the dial. These latter adjustments must follow the setting of the clock. Also additional pointers must be adjusted to the desired high and low temperature levels. Thus, there are a total of five mechanical adjustments needed, involving aligning pointers or the like on one or more dials with different index markings, making the entire set-up procedure a complex and tedious operation.